Sample preparation for analytical testing frequently, if not most typically, requires sample dilution under exacting conditions. Most important to an automated batch dilution sample preparation system is the factor of repeatability. Thus, it is required for analytical precision that the sample/diluent ratio be fixed and maintained exactly.
Typical prior art systems that depend on exacting tolerances to fix sample diluent ratios, including most commonly, precision metering pumps, capillary flow control devices, critical stream valving devices and the like, are generally, if not characteristically, sensitive to minute flow irregularities. As such, adequate precision control typically requires frequent fine adjustments to balance and establish a fixed flow ratio. Consequently, less than entirely adequate suitability is shown in respect to the performance desired for a generally unattended and automated process sample taking and sample preparation system.
Also, in cases where the diluent is flammable or toxic to the environment, or from an expense standpoint, since analytical grade materials are typically specified, it will be observed that sample preparation systems, as devised in the past, frequently require excessive diluent waste. Thus diluent drains are generally observed as a part of such systems. This condition, quite apparently considered necessary for utility in quite a large number of prior systems, is objectionable standing alone, and even much more so for largely unattended on-stream process applications.